Backups Jobs remains in state waiting for media

HI,

Since 3 days, backups have been taking a long time for complete. Its remains in the state "waiting for media" even though the vtl are available and with enough space. 
the vtl are on drives of compellent volumes via hba. The access to volumes has no problems. even i can explore these drives without problems and no delays.
for example, phase 2 of a backup its copied to a vtl, but for more than 12 hours has no complete and i have to abort.
Also phase 2 to tape takes a long time reading from a vtl.